Boris Johnson has apologised in public for calling black people "piccaninnies" and referring to their "watermelon" smiles.

The Tory Mayoral candidate insisted he "loathed and despised" racism and his words, written more than five years ago, had been taken out of context.

In a lively Evening Standard debate on the mayoralty, the first of a series, he attempted to lay to rest the row over his comments by urging black Londoners to "move on" and focus on important policy issues like transport, policing and crime instead.

His remarks, first publicised by aides of Ken Livingstone, have overshadowed his campaign and fellow panellist Michael Eboda, editor of black newspaper New Nation, warned Mr Johnson at the Influentials debate that his words would continue to plague him. "Some of the articles and comments you've put together have been extraordinarily abusive of black people," Mr Eboda said.

"Those things to you are an extremely big obstacle to being able to work with what is almost 12 per cent of London's population."

Mr Eboda denied he was doing Mr Livingstone's work for him by attacking the Tory candidate. "Don't think this is something that has been produced by Livingstone, it's not. It's actually something that people feel, Boris."

Mr Johnson insisted it was "not in [his] heart" to make racist remarks and told a packed Cadogan Hall in Chelsea: "I do feel very sad that people have been so offended by these words and I'm sorry that I've caused this offence. But if you look at the article as written they really do not bear the construction that you're putting on them.

"I feel very strongly that this is something which is simply not in my heart. I'm absolutely 100 per cent antiracist, I despise and loathe racism."

He added: "I do think it's very sad that a debate about the future of London is being reduced to this. There's a real risk if we keep going on about this kind of thing that people will think we're trivialising the debate about the future of their city and people want to hear about housing and transport and crime.

"They want to have a Mayor who speaks up for all Londoners and doesn't try to put people in boxes and divide and rule and endlessly go on about racism and race politics."

Panellist Nick Cohen, a journalist, warned Mr Eboda to "be careful" about taking Mr Livingstone's side as the Mayor had his own record of "revolting" comments.

He cited the Mayor accusing Equalities chief Trevor Phillips, who is black, of "pandering to the Right" so much that "soon he'll be joining the BNP" as well as Mr Livingstone's likening Jewish Evening Standard reporter Oliver Finegold to a "concentration camp guard".

However, Mr Eboda insisted: "I'm not on Livingstone's side, not in any way, shape or form."

The panel, which also included journalists Simon Jenkins and Yasmin Alibhai-Brown, discussed crime, transport, housing, the London Assembly's inability to hold the Mayor to account and boosting the youth vote. Mr Johnson suggested referendums on issues such as smoking in public places could make young people feel they had an impact.

"I wonder whether it's absolutely necessary for Whitehall to decide whether smoking should be banned in bars and clubs and restaurants," he said.

"I'm not a smoker, I disapprove of it, but I think this is something that could pre-eminently be decided locally."

He defended his appearances on the BBC comedy quiz Have I Got News For You, which prompted concern over how seriously he was taking his candidacy, by claiming it helped him to get his message across. "Politicians need to make much more effort and that is, of course, why I have gone onto TV quiz shows," he said. "I think this exercise is justified if, in the course of it, you connect with people on some level and they listen to you about issues. That's how I can defend what I do."

Simon Jenkins agreed the mayoral campaign, with its emphasis on personality politics, could attract young people to the ballot box in a way that national politics did not.

He urged greater devolution-of power to local councils, includinga mayor for every borough, to make young voters feel they had more control over their lives. "All politics starts locally and until we get back to that we're never going to get young people becoming involved in politics," he said.

The panellists had a lively debate on "affirmative action" - a policy proposed by Bevan Powell, deputy chairman of the Met's Black Pol ice Association - to increase the number of black people recruited to the police.

Ms Alibhai-Brown said it should be used for certain "key positions" but added that it might breed resentment and Mr Eboda argued it was only right to "try to level the playing field" a little.

Mr Johnson said he was in favour of the policy but claimed targets and quotas were unnecessary as they were "too prescriptive".

Mr Cohen claimed that many black and Asian middle-class people actually benefited from their ethnicity in the workplace. He remarked: "The only affirmative action no one ever talks about is affirmative action on behalf of the working classes."